1. Field of the Invention
The present invention relates generally to fluid flow control devices, and more particularly, but not by way of limitation, to a remotely operated discharge control system for use with the discharge systems of a tank for storing liquefied compressed gases and a cargo tank motor vehicle used to transport liquefied compressed gases.
2. Brief Description of the Related Art
Cargo vehicles used to transport liquefied compressed gases, such as propane, butane, gasoline, and diesel fuel, are required by law to have an emergency shutdown system which will terminate product discharge from the cargo tank in the case of a mechanical failure of hosing, fittings, or couplings which results in a spill. This emergency shutdown system is often in the form of an emergency handle mounted on a portion of the vehicle and coupled to a liquid control valve and a vapor control valve via a cable system. The valves are caused to close upon an operator pulling the emergency handle.
The problem encountered with such an emergency shutoff system is that the operator must have access to the emergency handle. However, the discharged gas is often highly flammable. Therefore, the operator may not be able to gain access to the emergency handle without risking injury to himself if the discharged gas has been ignited. Consequently, a system has previously been proposed for actuating the emergency shutdown system from a position remote from the vehicle.
This system is disclosed in U.S. Pat. No. 5,263,824, issued to Waldbeser et al. Waldbeser et al. discloses the use of a pulling solenoid connected to the cable system so that upon actuation of the solenoid, the cables are pulled and the valves are closed. The solenoid is connected to a vehicle mounted receiver which is capable of receiving signals from a hand-held transmitter. The receiver is additionally connected to the vehicle's ignition system so that the vehicle's engine is shut down to prevent ignition of the discharged gas by the vehicle's ignition system.
While the Waldbeser et al. system appears to be a satisfactory solution, problems are nevertheless still encountered in that the reliability of a pulling solenoid to actuate the cable system under all conditions, such as when the cable system is coated with mud or ice, is suspect.
In addition to the concerns associated with the unloading process, operators are faced with similar concerns while loading the cargo tank. That is, the tank receives liquefied compressed gas from a primary storage tank via a liquid line and a vapor line. A valve is interposed in each of these lines. Like the liquid discharge valve and the vapor valve discussed above, the valves interposed in the liquid line and the vapor line are coupled to an emergency shutdown system which generally includes a cable system actuated a distance from the valves. Also like the emergency shutoff system of the cargo vehicle, the operator may not be able to gain access to the emergency shutoff system of the storage tank, and if he can, he cannot be in two places at once. In other words, because the emergency handle of the vehicle is often located away from the emergency handle of the primary storage tank, the operator cannot pull the emergency handle for the vehicle and the primary storage tank simultaneously.
To this end, the need exists for an improved emergency discharge control system that allows an operator to terminate product discharge from the cargo tank and the storage tank from a safe, remote distance and which will effectively operate in harsh conditions. It is to such a system that the present invention is directed.